The present invention relates to devices for controlling a distribution of power to subsystems, for example to a main device and at least one secondary device or a plurality of secondary devices.
More particularly, the present invention relates to the above mentioned devices formed as electrical power strips and power control sensors which can be used with new devices having two modes of operation, standby or off and full on, with the use of main device or secondary devices.
One type of an electrical distribution device is the power strip or power control center, which generally comprises of a row of power outlets, switched or unswitched, to distribute power to a primary device and secondary device(s) from a standard outlet (e.g., wall outlet). Some power strips and control centers contain options like circuit breakers, fuses and/or surge protectors, for example.
In newer personal computers the system can turn itself off and is controlled by the operating system. During the system shutdown, there is a delay in which the operator must wait for the system to finish before turning off the secondary device(s). Depending on the operating software and programs, this can be a long time. Using this invention, the user may leave after the shutdown is started. When the system finishes and switches off or to the standby mode, the secondary device(s) will be turned off.
When used with computer devices, each device is plugged into a separate outlet with the computer plugged into the main outlet. When the computer is turned on, the current level increases to a high enough level to turn on the secondary device(s). Other constant power outlets may also be included for wake up devices, such as modems capable of bringing the system out of standby mode.
U.S. Pat. No. 4,659,941 discloses a power strip where the main outlet current controls the secondary device(s) as shown in FIG. 2. Here, the secondary switch and trigger device are the same. In this configuration, the main device must draw current at the start of each cycle of line power for the triac to trigger correctly. With high efficiency supplies, this is never the case because they only draw power during the peak voltage of the line power. So, when used with a PC or newer video/audio equipment, the voltage to the secondary outlets will not be a sine wave like the voltage from the wall outlet. This waveform can damage the secondary device(s). The second problem is personal computers and newer video/audio equipment do not turn off completely, but remain in a standby mode so they can turn themselves on at a given time or occurrence. Because of this, the secondary device(s) will never be turned off, defeating the purpose of the power strip""s use.
U.S. Pat. Nos. 4,731,549 and 4,970,623 are methods for controlling secondary device(s). Both require internal power supplies and many components, making them too expensive for mass production and difficult to fit in a standard power strip.
Accordingly, it is an object of present invention to provide a device for controlling distribution of power to subsystems, which avoids the disadvantages of the prior art.
In keeping with these objects and with others which will become apparent hereinafter, one feature of present invention resides, briefly stated, in a device for controlling a power distribution to subsystems which has a power input to connected to a power source, a primary power output to be connected to a primary device, at least one secondary power output to be connected to at least one secondary device; sensing means for sensing when a current level falls below a threshold in response to the primary device being turned off and when the level current raises above a threshold in response to the primary device being turned on; executing means operatively connected with said sensing means and operative for interrupting a power supply to said at least one secondary device when the sensing means sense the current level below the threshold and supplying power to said at least one secondary device when said sensing means sense the current level above the threshold; and means for limiting voltage across said sensing means so as to limit heat produced by said sensing means but at the same time to allow tripping of said sensing means.
In accordance with a further feature of present invention, the inventive device further has time delay means which is located between said sensing means and said executing means and is operative for delaying interruption of power supply or supply of power to the at least one secondary device in response to the sensing of the current level below the threshold or above the threshold by the sensing means correspondingly. The time delay means can be formed as a capacitor and resistors arranged between the sensing means and the executing means.
In accordance with a further embodiment of the present invention, the sensing means can be formed as a current sensing resistor arranged in series with a power input of the device and a triac connected to the resistor, for example through another resistor.
The executing means can be formed for example as a solid state DC relay, as an AC mechanical relay, as a solid state AC relay, etc.
The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.